The earliest light emitting diode was launched in 1965 and emitted red light. The earliest LED used Gallium Arsenide (GaAs) as a base material, which had luminous efficiency (luminous flux) of only 0.1 lumen per watt.
Phosphor used as a spectrum conversion has been broadly applied to LED since 1968. In 1996, Japan Nichia announced cerium-doped yttrium aluminum garnet (YAG:Ce) was excited by blue light LED to emit yellow light and is further combined with blue light to form cold white light.
With the improvements on package technology and luminous efficiency of LED, LED of compact volume, low current consumption, long life and rapid reaction to operation has come out, too.
Furthermore, owing to the requirement of carbon reduction and the raising awareness of environment protection, LED has been step-by-step replacing traditional incandescent light bulb and mercury lamp in many countries of the world. Now LED has applied broadly to signal light, advertisement light, vehicle light source, outdoor lighting or home lighting, display or backlight light source for computer peripheral devices.
Phosphor demand has been increased with the population of LED, the demand for rare earth metals such as Yttrium and Europium for phosphor has been increased in a rapid speed. Nowadays, the global rare earth metals are distributed in China (30.86%), the United States (14.88%), Australia (5.99%), the Independence States (21.67%), India (1.30%), Brazil (0.10%), Malaysia (0.03%) and other domains (25.17%).
Owing to the raising awareness of environment protection and high mining cost, the United States stopped extracting the rare earth metals since 1980. Now China that owns the 97% of the global rare earth metals yield is the biggest supplier of the rare earth metals. Though the rare earth metals are not deficient currently, however, their supplying chains are shrunk because China restricts its output of the rare earth metals. As a result, it is necessary to recycle the used rare earth metals in markets for efficiently stabilizing the raising prices of the rare earth metals.
So far, phosphor can be manufactured by solid state diffusion method, hydrothermal method or sol-gel method. Very high reaction temperature is necessary for the solid state diffusion method and the hydrothermal method. The sol-gel method is not suitable for mass production because it needs metal alkoxides of high prices and long time for manufacturing.
Accordingly, it is an issue of the present invention to form a kind of phosphor composition that is easy to be prepared and has low consumption on the rare earth composition.